1. Field of the Invention
The present invention relates to a one-port elastic wave resonator in which interdigital transducer (IDT) electrodes are provided on a piezoelectric substrate. The present invention also relates to an elastic wave filter device and a duplexer including the above-described one-port elastic wave resonator.
2. Description of the Related Art
Up to now, surface acoustic wave resonators have been widely used for resonators which form a filter device. In the one-port surface acoustic wave resonator described in “A Triple-Beat-Free PCS SAW Duplexer”, (IEEE Ultrason. Symp., pp. 67-70, 2012), an IDT electrode is divided into sections connected in series. Here, a first IDT electrode and a second IDT electrode are connected in series with each other. The areas of the first and second IDT electrodes have been increased so as to realize an impedance that is the same as that in the case of no division. As a result, the energy density within the first and second IDT electrodes is lowered, and distortion due to nonlinear signals is reduced.
On the other hand, Japanese Unexamined Patent Application Publication No. 2004-320411 discloses a surface acoustic wave device for increasing thermal shock resistance. In this surface acoustic wave resonator device, two surface acoustic wave resonator portions are formed on a piezoelectric substrate. The two surface acoustic wave resonator portions are electrically connected in parallel with each other. In other words, the first and second IDT electrodes forming the first and second surface acoustic wave resonator portions are electrically connected in parallel with each other.
The surface acoustic wave device described in “A Triple-Beat-Free PCS SAW Duplexer”, (IEEE Ultrason. Symp., pp. 67-70, 2012) allows nonlinear distortion to be reduced. However, the first and second IDT electrodes have increased areas. Hence, a reduction in size was difficult.
On the other hand, the surface acoustic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2004-320411 employs a parallel connection structure to increase thermal shock resistance. With this structure, nonlinear distortion can be suppressed without increasing the areas of the IDT electrodes. However, with the parallel connection structure disclosed in Japanese Unexamined Patent Application Publication No. 2004-320411, wiring lines for connecting the first and second IDT electrodes occupy a large space. Hence, a reduction in size is difficult also with this structure.